(456a) Computational Screening of Metal-Organic Frameworks Suitable for Thermal Energy Storage Applications with Low Global Warming Potential Refrigerants

The demand for refrigeration and air-conditioning is likely to increase in the coming years due to global warming and boost of wealth in tropical regions. These processes already account for around 17% of the global electricity consumption [1], while current high Global Warming Potential (GWP) refrigerants used in these equipment have a great impact in climate change. Therefore, efficient and environmentally friendly refrigeration cycles are of utmost importance. Adsorption refrigeration has been proven an excellent potential candidate for replacing conventional, energy-intensive vapour compression refrigeration cycles [2,3] In adsorption refrigeration systems, the cooling effect is driven by the thermal energy produced and injected into an adsorbent bed. The adsorptive process enables to replace mechanical compressors in vapour-compression cycles, reducing energy consumption. In addition, adsorption refrigeration facilitates the use of renewable energy sources, which are expected to increase in the near future [4]. Adsorption refrigeration can be used as cold thermal energy storage (CTES) and thermal energy storage (TES) units [5], accumulating exceeding cooling or heating capacity, which can be used when needed.

In CTES and TES applications, the choice of a suitable adsorbent-refrigerant working pair plays a crucial role. We will present results concerning the first computational screening of experimentally available metal-organic frameworks (MOFs) for CTES and TES units using three low GW refrigerants: R1234yf, R1234ze(E) and the blend R513A, in order to search for the best MOF-refrigerant pair for this application. The choice of these refrigerants is based on the need to deploy low GWP refrigerants after the ratification of Kigali’s agreement [6], suitable for different cooling applications. The third generation refrigerant R134a currently in use in refrigeration systems is also considered for comparative purposes. We conducted Grand Canonical Monte Carlo simulations to establish a relationship between the adsorptive capacity and material properties. At total of 40 MOFs, belonging to several representative structural families were studied, including IRMOFs, M-MOF-74, ZIFs, COFs, NUs, and MILs topologies [7]. Results show that MOFs with open metal sites have a strong interaction with R1234yf and R1234ze(E), making them more suitable for TES. Conversely, MOFs presenting large pore size, such as Cr-MIL-101 and IRMOF-10, MOF-200, have a low affinity for HFO and large working capacities, showing a considerable higher CTES energy density that the currently used activated carbons/R134a pairs. It is also observed that the M-MOF-74 family is not suitable for CTES under the given operating conditions, but some of them maybe appropriate for TES applications.

Overall, the MOF-200/R513A pair is a promising candidate for TES and CTES units considering its low selectivity, combined with a high TES and CTES energy density and relatively high regenerability. In addition, given its selectivity for HFOs vs HFC, UIO-66 is a good candidate to be experimentally investigated for the separation of R1234yf/R134a mixtures. Once the top performers were selected from the screening, detailed calculations of these MOFs/refrigerant pairs, with optimized operating conditions were performed and results will be presented and discussed here.

We acknowledge support for this work from Khalifa University of Science and Technology (projects CIRA2018- 121 and RC2-2019-007)

References

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[2] Wang, R.; Wang, L.; Wu, J. Adsorption Refrigeration Technology: Theory and Application; John Wiley & Sons, 2014.

[3] Fernandes, M. S.; Brites, G.; Costa, J. J.; Gaspar, A. R.; Costa, V. A. F. Review and Future Trends of Solar Adsorption Refrigeration Systems. Renew. Sustain. Energy Rev. 2014, 39, 102–123.

[4] Jacobson, M. Z.; Delucchi, M. A.; Bazouin, G.; Bauer, Z. A.; Heavey, C. C.; Fisher, E.; Morris, S. B.; Piekutowski, D. J.; Vencill, T. A.; Yeskoo, T. W. 100% Clean and Renewable Wind, Water, and Sunlight (WWS) All-Sector Energy Roadmaps for the 50 United States. Energy Environ. Sci. 2015, 8 (7), 2093–2117

[5] Lefebvre, D.; Tezel, F. H. A Review of Energy Storage Technologies with a Focus on Adsorption Thermal Energy Storage Processes for Heating Applications. Renew. Sustain. Energy Rev. 2017, 67, 116–125.

[6] United Nations Treaty Collection. Kigali, (2016).

[7] E.J. Garcia, D. Bahamon, L.F. Vega, Systematic Search of Suitable Metal–Organic Frameworks for Thermal Energy-Storage Applications with Low Global Warming Potential Refrigerants. ACS Sustainable Chem. Eng. 2021, 9, 8, 3157–3171.